AJP - Gastrointestinal and Liver Physiology, Vol 252, Issue 2 281-G286, Copyright © 1987 by American Physiological Society
Characteristics of glycyl-L-proline transport in intestinal brush-border membrane vesicles
V. M. Rajendran, J. M. Harig and K. Ramaswamy
A proton-peptide symport mechanism has been postulated for transport of
dipeptides in rabbit intestinal and renal brush-border membrane vesicles
(BBMV). We have investigated the effects of a transmembrane potential (in
mouse) and an inwardly directed proton gradient (in mouse, rabbit, and
human) on the transport of glycyl-L-proline in intestinal BBMV. Membrane
potential alterations, induced by permeant anions or generated by a
K+-diffusion potential in the presence of valinomycin, did not accelerate
the uptake of glycyl-L-proline. In contrast, in parallel experiments the
uptake of D-glucose, whose cotransport system is electrogenic, was markedly
increased by an interior negative membrane potential. Thus the transport of
glycyl-L-proline in mouse intestinal BBMV is not electrogenic. Further
studies on the effect of a proton gradient (extravesicular pH 5.5;
intravesicular pH 7.5) on transport of glycyl-L-proline revealed an absence
of stimulation of glycyl-L-proline transport and lower uptake rates in the
presence of a proton gradient. The simultaneous presence of an interior
negative membrane potential and an inwardly directed proton gradient did
not accelerate the transport of glycyl-L-proline. These results demonstrate
that the transport of glycyl-L-proline in mouse intestinal BBMV is neither
electrogenic nor energized by an inwardly directed proton gradient.
Likewise, pH gradients do not stimulate glycyl-L-proline uptake in either
rabbit or human BBMV.
